The invention relates to reversible liquid/solid phase change compositions (PCM). More particularly, the invention resides in phase change compositions for the storage of energy comprising a mixture of hydrated calcium bromide and hydrated calcium chloride having added thereto a modifier selected from the group consisting of KBr, KCl, and mixtures thereof.
The modifier which is employed with the hydrated CaBr.sub.2 /CaCl.sub.2 mixture of the invention is particularly effective to modify the semicongruent melting behavior of the mixture to reduce the formation of crystalline CaBr.sub.2 and CaCl.sub.2 hydrate phases other than the hexahydrate phase.
Preferably, the PCM of the invention also includes a nucleating agent which is particularly effective to reduce supercooling of the PCM to less than 3.degree. C. during retrieval of the stored energy by crystallization. The nucleating agents which have been found to be effective in the quaternary or quinary PCM's of the invention are selected from the group consisting of SrCl.sub.2, Ba(OH).sub.2, BaO, SrBr.sub.2, Sr(OH).sub.2, SrI.sub.2, BaI, BaCO.sub.3, SrCO.sub.3, and mixtures thereof.
The invention also resides in the use of the PCM of the particular composition as herein described in an energy stored device and in the method of storing energy.
The phase change compositions of the invention are useful over a broad temperature range of from about 5.degree. to about 50.degree. C. and thus can be employed (1) for the storage of "coolness" over a temperature range of from about 5.degree. to about 17.degree. C.; (2) for the storage of "heat" over a temperature range of from about 25.degree. to about 50.degree. C., and (3) as a buffer or heat sink to modulate diurnal swings in the ambient temperature range of from about 17.degree. C. to about 27.degree. C.